and I'm going to replace it with synthetics:

Amsoil 0w-20 100% synthetic
EaO 9 oil filter

For the trans, it'll be 75w-90 GL4 gear lube.

With tax/shipping, it'll cost me less than $95.

This is the my first time owning/working on a manual trans car.

Will I see an improvement in mileage?

Will the synthetic gear lube give me smoother shifts?

The gear lube is just drain and fill, right? No filter or anything like that to worry about?

I've found that they spec 30 ft./lbs. for the drain plug and 36 ft./lbs. for the gear lube plug.

Is that right?

 

DIY-redline mt-90 transmission fill
https://www.scionlife.com/forums/viewtopic.php?t=120673

As for the engine oil I put in regular oil at 2,000 then at 5,000 I will switch to mobil 1 synthetic

Engine oil wise I would highly recommend a search because it has already been discussed enough to fill a novel.